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Reactive Strength Index Made Simple

A Simple Practical Guide for Athletes, Patients, and Coaches – Written by Francis Wheeler – Physiotherapist

What is RSI and RSI-mod?

Reactive Strength Index (RSI) is a metric used to assess how efficiently someone can produce and redirect force in a short time—essentially, how “spring-like” they are.

– RSI = Jump Height / Ground Contact Time (typically from a Drop Jump)

– RSI-mod = Jump Height / Time to Takeoff (used in Countermovement Jump)

RSI is like measuring how fast a compressed spring can rebound—the faster and higher the jump, the stronger the reactive strength. These measures are valuable for assessing performance, risk, recovery, and neuromuscular function.

How Do We Test RSI?

RSI can be captured via several jumping tests:

Countermovement Jump (CMJ)

– Focus on RSI-mod with the measure starting from beginning of the movement and ending at the landing phase.

– More specifically measures concentric explosiveness.

– Can also be completed single leg but the accuracy of the reading changes as there are more variables to be considered.

Countermovement Jump and Force trace for a Countermovement Jump Test

Bilateral Hop (10/5)

– Assesses leg stiffness and rhythm by repeating 10 hops and taking the best 5 to get an average reading.

– Useful for evaluating fatigue and symmetry between limbs in a repeated bilateral action.

Force trace for a 10/5 Bilateral Hop Test

Single-Leg Hop Test (10/5)

– Like the bilateral test but highlights asymmetries between limbs with the combined view of contact time and height without the ability to over-compensate with one side vs another.

– Common in rehabilitation and return to play decisions for lower limb injuries.

Force trace for a 10/5 Single leg Hop Test – Tests combined

Drop Jump

– The original RSI test that measures the ability to transition from falling to jumping with strong a correlation to change of direction.

– More specifically targets the stretch-shortening cycle and reactivity.

– Can complete single leg just like the CMJ but suffers from some similar difficulties to draw consistently accurate measurements.

Drop Jump and the Force trace for a Drop Jump

RSI and Injury Risk

Lower RSI values may suggest poor elastic return, reactive control/ability, or neuromuscular function, which can be associated with ACL injury risk, Achilles tendinopathy, and Hamstring re-injury risk among others.

Monitoring RSI and asymmetry between limbs can help guide the rehab progress and readiness for return to sport.

RSI and Fatigue Profiling

RSI is sensitive to neuromuscular fatigue and often decreases before strength metrics change. Although peak forces may be similar, or the same amount of weight could be moved, the speed and reactive elements are often compromised.

This is often used as a tool in sport to gauge a player’s post-match fatigue levels or how ready/recovered they are to guide decision making on training intensities and game time.

A baseline measurement is often taken at the start of the season which is then used to compare against to help objectively guide decisions around player management with hopes to act as a tool to help reduce injury risk in season.

RSI and Power Output

RSI reflects not just how much force is produced, but how quickly it’s expressed – making it vital for explosive movements like sprinting and change of direction.

It helps identify speed-dominant vs. strength-dominant profiles and informs plyometric training to build optimal performance.

Training to Improve RSI

Improvement focuses on optimizing force expression, speed and minimizing contact time. Coaching cues should emphasize quick/short ground contact and intentional explosive effort to get the most out of the exercise and tests.

Jump-Based:

– CMJ variations

– Band-assisted jumps

– Weighted jumps

– Speed Squats

Hop-Based:

– Pogo hops

– Single-leg stiffness drills

– Bounding progressions

Drop-Based:

– Depth jumps

– Drop-to-jump transitions

– Altitude landings

Conclusion

RSI is a flexible and often underutilized metric in both rehab and performance settings. It can guide rehabilitation, return-to-play decisions, fatigue management, and individualized training programs.

Here at Harris and Ross we are trained in the use of VALD Force Plates which give a quick, detailed, and highly accurate reading. Alternatively, there are various apps (eg: MyJump) and other devices that can help with RSI assessments.

Various tools for RSI testing include:

– Mobile apps (e.g. MyJump)

– Contact mats

– Force plates

One of the various formats we can easily visualize information from our VALD technology on the VALD Hub.

RSI Benchmarks Across Populations

Below is a bit of a general breakdown of some RSI norms for normal, trained athletic, and elite populations. There are many other variables to consider (age, sport/activity type etc) but this information can be used for quick take-aways and comparisons.

Test: Countermovement Jump (RSI-mod)

Metric Description: Jump Height ÷ Time to Takeoff

– Normal Population:

– Male: ~0.40–0.50

– Female: ~0.30–0.40

– Trained Athletes:

– Male: ~0.55–0.65

– Female: ~0.45–0.55

– Elite:

– Male: >0.70

– Female: >0.60

Test: Drop Jump

Metric Description: Jump Height ÷ Ground Contact Time

– Normal Population:

– Male: ~1.5–2.0

– Female: ~1.2–1.8

– Trained Athletes:

– Male: ~2.0–2.5

– Female: ~1.8–2.2

– Elite:

– Male: >2.5 (some >3.0)

– Female: >2.0

Test: Bilateral Hop (10/5 Test)

Metric Description: Mean of top 5 jumps

– Normal Population:

– Male: ~1.5–1.8

– Female: ~1.3–1.6

– Source:

– Trained Athletes:

– Male: ~1.8–2.2

– Female: ~1.6–2.0

– Source:

– Elite:

– Male: >2.0

– Female: >1.8

– Source:

Test: Single-Leg Hop (10/5)

Metric Description: Mean of top 5 jumps

– Normal Population:

– Male: ~1.0–1.3

– Female: ~0.8–1.1

– Trained Athletes:

– Male: ~1.3–1.5

– Female: ~1.1–1.3

– Elite:

– Male: >1.5

– Female: >1.3

Metric Sources:

Reactive Strength Index Made Simple

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